WO2008087537A2

WO2008087537A2 - A support net for underground mine supports

Info

Publication number: WO2008087537A2
Application number: PCT/IB2008/000108
Authority: WO
Inventors: Nils Mittet SKARBÖVIG
Original assignee: Skarboevig Nils Mittet
Priority date: 2007-01-18
Filing date: 2008-01-18
Publication date: 2008-07-24
Also published as: WO2008087537A3; ZA200800630B

Abstract

An underground support (40, 52) is provided of the type in which a permeable geotextile material is employed as a curtain (46) or bag (52) to retain uncemented or cemented granular material or other grout (42) in its operative position between a hanging wall and a footwall in an underground mine. A support net extends over at least predetermined areas of the geotextile material wherein the support net is made of two crossed arrays of yarns (26, 28) secured together at their points of intersection with all the yarns of one array thereof extending in a generally horizontal direction and the yarns of the other array thereof extending in a generally vertical direction in the operative position. A method of manufacturing a support net is also provided as well as support nets for use in such an underground support.

Description

A SUPPORT NET FOR UNDERGROUND MINE SUPPORTS

FIELD OF THE INVENTION

This invention relates to a support net for underground mine supports and, more particularly, underground mine supports of the type that employ a geotextile for retaining uncemented or cemented backfill or other grout in situ between the hanging and foot walls in underground mining operations.

BACKGROUND TO THE INVENTION

The support of the hanging wall in stopes is one of the most basic requirements in underground mining operations. Dependant on the type and quality of rock being supported, the depth of mining, the prevalent field stresses, seismicity, stoping width and a number of other factors, stope support can vary across a vast range of materials, configurations and systems. These include, amongst others, timber poles, timber and composite packs, steel props, unmined ore pillars, rock anchors and granular or tailings type supports. Of the granular support media, uncemented or cemented backfill and grout packs are among the most routinely used support products.

Granular backfill materials or grout packs are usually retained by a curtain of geotextile material or contained within a suitable geotextile bag, depending on the configuration of the support. The geotextile material is usually woven or knitted from a low tenacity polymer fibre and itself offers little lateral confinement as its stretches easily under load. Its primary function is to provide suitable containment for the grout slurry with optimal drainage and filtering properties. As they are relatively weak, backfill curtains or grout bags have to be prevented from bulging and bursting both during filling under hydrostatic pressure as well as under lateral dilation during loading after the material has set or cured.

Secondary support netting or meshing is used for this purpose as it provides the necessary tensile strength to prevent the geotextile from rupturing prematurely. At present, wire diamond mesh or steel weld mesh is used of the fact that it is both expensive and difficult to transport.

It is to be mentioned that in so far as grout packs are concerned in which a vertically spaced series of retaining hoops are suspended around a grout bag by means of netting made from knotted yarns, the netting is used in the orientation in which it is produced namely with the yarns extending in crossed diagonal relationship to each other. Flexible yarn netting used in this orientation does not provide satisfactory support to a grout bag because of the tendency to stretch under load as illustrated in Figures 1A and 1B.

A typical net (1 ) has a rectangular shape with two arrays of yarns (3, 4) intersecting each other at an incline to the peripheral edges (5, 6, 7, 8) of the net (1 ), that is, in the direction of the diagonal. Loading the net (1 ) in its length (indicated by arrow (10)) causes elongation thereof, as shown in Figure 1 B, and consequent narrowing towards the centre thereof. Loading along its width (as indicated by arrow (11 )) produces a similar effect except that the width becomes elongated. Consequently, they are not considered as offering adequate support against rupturing and accordingly do not substitute for the wire diamond mesh or steel weld mesh.

OBJECT OF THE INVENTION

It is an object of this invention to provide a support net made from knotted yarns or the like which will, at least to some extent, be suitable for replacing the wire diamond mesh or steel weld mesh as a support for the geotextile. SUMMARY OF THE INVENTION

In accordance with one aspect of the invention there is provided an underground support of the type in which a permeable geotextile material is employed as a curtain or bag to retain uncemented or cemented granular material or other grout in its operative position between a hanging wall and a footwall in an underground mine with a support net extending over at least predetermined areas of the geotextile material, the underground support being characterised in that the support net is made of two crossed arrays of yarns secured together at their points of intersection with all the yarns of one array thereof extending in a generally horizontal direction and the yarns of the other array thereof extending in a generally vertical direction in the operative position.

Further features of this aspect of the invention provide for the support net to be generally rectangular in shape with the sides of the rectangle being parallel to the directions in which the arrays of yarns extend; for the yarns to be knotted together at their points of intersection; for the yarns to be twisted or braided and for the yarns to be made from a polymeric material such as high density polyethylene and polypropylene or mixtures thereof; for reinforcing, typically in the form of a rope, to be provided about at least the periphery of the support net; and for the further reinforcing to further extend across the support net at spaced positions.

In accordance with a second aspect of the invention there is provided a method of producing a support net for use in an underground support wherein knotted yarn netting is produced on a loom in a manner in which it emerges from the loom with the yarns extending in two arrays thereof that extend diagonally relative to each other, the method being characterised in that the knotted yarn netting is then cut along lines extending parallel to each of the arrays of yarn to produce a support net in which the two arrays of yarn extend parallel to the sides of the support net. The invention also provides a support net formed from two crossed arrays of yarns secured together at their points of intersection, the support net being characterised in that it is cut from a net produced on the diagonal such that the arrays extend normally to each other with substantially all the yarns of one array extending between opposite peripheral edges of the net.

Yet further features of the invention provide for securing means to be provided on the net, preferably on the peripheral edges thereof, for securing the support net in position.

In order that the invention may be more fully understood different embodiments thereof will now be described with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:-

Figures 1A and 1B are front elevations of a conventional net produced with the arrays of yarns extending diagonally relative to each other;

Figure 2 is a front elevation of one embodiment of a support net according to the invention;

Figure 3 is a front elevation of a second embodiment of a support net according to the invention;

Figure 4 is a perspective view of the support net in Figure 3 in use; Figure 5 is a perspective view of third embodiment of a support net according to the invention in use; and

Figure 6 is a schematic illustration a method of making a support net according to the invention.

DETAILED DESCRIPTION WITH REFERENCE TO THE DRAWINGS

A support net (20) is shown in Figure 2 and has a rectangular shape with a pair of opposite peripheral edges (22, 24). The net (20) is formed, in conventional fashion, from two arrays (26, 28) of intersecting yarns knotted together at their points of intersection. In this embodiment of the invention, the yarns are formed from a braided polymeric material such as 4 millimetre high-density polyethylene braid. As provided by this invention, the arrays (26, 28) are normal to each other with all the yarns in the one array (26) extending between two opposite peripheral edges (22) and all the yarns of the other array (28) extending between the other opposite peripheral edges (24) of what is a generally rectangular support net.

Typically, the spacing of the yarns in the two arrays is the same so as to provide square apertures that can vary in size from say about 80 millimetres by 80 millimetres to about 150 millimetres by 150 millimetres. The overall size of the support net would typically be, in the case of a Paddock net, anything from about 800 millimetres to about 1400 millimetres wire by about 10 metres to about 30 metres in length.

It has been found that the support net (20) is substantially stiffer in its response to force acting on it at right angles to the plane of the arrays (26, 28) and does not contract either in its width or length. It also shows minimal stretching when force is applied along its length or width. As shown in Figure 3, the support net (20) can be reinforced by securing a rope (30) about its periphery as well as rope (32) across its width and rope (34) across its length. Such a rope could conveniently be a 5 millimetre diameter polypropylene/polyethylene mix known as Danline.

As shown in Figure 4, the net (20) can be used in a backfill paddock (40) in which the backfill (42) is contained behind a geotextile curtain (46) which is supported by a number of timber props (44) at its down-dip end. The net (20) is simply secured to the timber props (44) adjacent of the geotextile curtain (46). To this end, any suitable tie, including wire or rope can be used. Preferably, however, fabric ties will be fitted to the periphery of the net (20).

In this embodiment, a reinforcing rope (34) as described with reference to Figure 3 is used on the support net (20). It has been found that the support net (20) is highly effective in preventing excessive bulging and possible bursting of the geotextile curtain (46) during filling and loading in this application.

The support net of the invention is far easier to handle underground than wire diamond mesh or welded wire mesh and is also much more cost effective in terms of its strength to weight ratio. Transport and storage is also very much easier.

As shown in Figure 5, the support net (50) could be tubular in shape to enable it to fit over a cylindrical geotextile bag (52). In this configuration, the support net (50) only has one pair of opposite peripheral edges (54) with the yarns of one array (56) extending between these. The yarns (58) of the other array (58) each form a loop. Clearly, however, the support net (20) and that is illustrated in Figure 2 could also be used in this application by wrapping it around the bag (52) and securing the opposite peripheral edges (24) together or overlapping these and securing the overlapping portions together. It will be appreciated, however, that many other embodiments of a support net exist which fall within the scope of the invention. For example, any suitable yarn can be used particularly as regards its strength, weight and material of construction. Also, any suitable mesh opening and geometry can be used.

Advantageously, a conventional loom can be used in the manufacture of support nets according to the invention. Referring to Figure 6, a loom (60) is used to produce a continuous sleeve-shaped net (62) with the yarns inclined diagonally to the length thereof. Conventionally, nets are obtained by taking cuts extending at right angles through the sleeve length, that is, diagonally across the individual apertures of the mesh. According to the invention, however, a spirally extending panel (64) of required dimension is cut from the sleeve to provide a support net by cutting the panel edges along lines extending parallel to the yarns of the arrays thereof. The result is that the yarns extend at generally right angles between opposite sides of the resultant support net as described above. Not only does this contribute to cost effective manufacture of support nets of the invention but also enhances the utility of existing net manufacturing looms.

It will, however, be understood that any suitable method of manufacturing a support net according to the invention can be used and the intersecting yarns need not be knotted together but could be secured together in any other convenient fashion, including through the use of fasteners.

Claims

CLAIMS:

1. An underground support (40, 52) of the type in which a permeable geotextile material is employed as a curtain (46) or bag (52) to retain uncemented or cemented granular material or other grout (42) in its operative position between a hanging wall and a footwall in an underground mine with a support net extending over at least predetermined areas of the geotextile material, the underground support being characterised in that the support net is made of two crossed arrays of yarns (26, 28) secured together at their points of intersection with all the yarns of one array thereof extending in a generally horizontal direction and the yarns of the other array thereof extending in a generally vertical direction in the operative position.

2. An underground support as claimed in claim 1 in which the support net is generally rectangular in shape with the sides of the rectangle being parallel to the directions in which the arrays of yarns extend.

3. An underground support as claimed in either one of claims 1 or 2 in which the yarns are knotted together at their points of intersection.

4. An underground support as claimed in any one of the preceding claims in which the yarns are twisted or braided polymeric material.

5. An underground support as claimed in any one of the preceding claims in which reinforcing in the form of a rope (30) is provided about at least the periphery of the support net and optionally, in addition, further reinforcing (32, 34) extends across the support net at spaced positions.

6. A method of producing a support net for use in an underground support wherein knotted yarn netting is produced on a loom (60) in a manner in which it emerges from the loom with the yarns extending in two arrays thereof that extend diagonally relative to each other, the method being characterised in that the knotted yarn netting is then cut along lines extending parallel to each of the arrays of yarn to produce a support net (64) in which the two arrays of yarn extend parallel to the sides of the support net.

7. A support net (20, 50) formed from two crossed arrays of yarns secured together at their points of intersection, the support net being characterised in that it is cut from a net produced on the diagonal such that the arrays extend normally to each other with substantially all the yarns of one array extending between opposite peripheral edges of the net.

8. A support net as claimed in either one of claims 7 and 8 in which securing means are provided on the net at or towards the peripheral edges thereof.